Motion detection is a process where a reference frame is searched for a block that is similar to a source block in a frame to be processed among a series of frames; and the difference in the spatial position between the block and the source block is output as a motion vector. To improve the precision of the motion detection, for example, evaluating as many candidate vectors as possible is required. On the other hand, when the number of candidate vectors increases, the amount of computation necessary for the motion detection increases and therefore, the processing time and the power consumption of the apparatus overall increase.
For example, according to a related technique, a sum-of-absolute-differences (SAD) computation is executed using pixels in a block of a frame and pixels in a comparative block of a search window in a frame that precedes the frame by one frame; and when the cumulative value of SAD values is greater than or equal to the smallest SAD value thus far, the SAD computation is discontinued. According to a signal processing method for executing motion compensation prediction between two images separated from each other in the time series, a block matching process that is executed in an unprocessed region in the search area after the sum of absolute differences of the pixel values reaches a predetermined threshold value for the first time, is forcibly terminated. The sum of absolute differences is an index for detecting the motion vector.
According to a technique referred to as “hierarchical search method”, motion detection is executed for a sub-sampled reduced image. In the hierarchical search method, for example, in a first stage motion detection process, an approximate motion vector is derived using an image acquired by a reduced original image; and in a second stage motion detection process, motion detection is executed for a search range centered about a point represented by the motion vector that is the result of the first stage motion detection, using the original image and a reference image. For examples of the above techniques, refer to Japanese Laid-Open Patent Publication Nos. 2007-183901, H10-271514, and H11-298904).
However, according to the conventional techniques, the amount of computation necessary for the motion detection still becomes enormous associated with increases in the number of candidate vectors. Consequently, a problem arises in that the processing time and the power consumption of the overall apparatus necessary for the motion detection increase.